Nonot to my knowledge,there are three long barces and then the side braces. then the two braces you are asking about go on each side of the center one bracing to the back directly.But Steve likes to build stuff strong so you may be ok with what your doing.

Akkk my mistake I was thinking about a SO.Your fine on what your doing. the compresion chamber on a Imperial is not bracedSo your bracing is just a bonus. because its not sealed in a Standard Imp flex is not as bad in the chamber.But you talking to a guy that only has built a cardboard one and a wood cardboard hybrid SO.Build em strong whenever you can..looks great.